Light-emitting elements are known in which, for example, a wavelength conversion member in which phosphor particles are dispersed in a resin such as epoxy or silicone is disposed in contact with a blue LED element. In recent applications, LEDs are increasingly replaced by laser diodes (LDs) which have a high energy efficiency and are easily adaptable to miniaturization and increase in output.
Lasers apply high-energy light to a local site. When laser light is focused onto a resin, the irradiated site is burnt. A known approach to this problem is to use all-inorganic wavelength conversion members that contain an inorganic binder in place of a resin which constitutes the all-inorganic wavelength conversion member (Patent Literatures 1 to 6).
Further, techniques associated with structural materials are disclosed in which ceramic particles having two grain sizes are combined to enhance packing uniformity and packing density (Patent Literature 7). Patent Literature 7 describes that a metal-ceramic composite preform is preferably formed using ceramic particles having two grain sizes wherein the ratio of the average particle size of finer particles is controlled to 6 to 20.